The invention relates to a luminaire, in particular for testing workpiece surfaces, which comprises at least two illuminants which emit electromagnetic radiation in different wavelength ranges.
The invention furthermore relates to a method for operating a luminaire, in particular for testing workpiece surfaces, if appropriate using a fluorescent marking medium.
DE 10 2004 043 295 B4, EP 1 623 213 B1 and U.S. Pat. No. 8,616,722 B2 disclose luminaires of the type mentioned in the introduction which comprise LEDs that emit white light and ultraviolet radiation. They are used for visual inspections of workpiece surfaces, in particular for detecting contaminants, for penetrant testing and for fluorescent magnetic powder testing. During visual inspection, in particular during testing of workpiece surfaces according to the fluorescent penetrant method, a fluorescent medium is used to make defects on workpiece surfaces visible by excitation with ultraviolet radiation. The inspection is usually carried out in the dark, with ambient illuminance of less than 20 lux, because human beings have higher contrast sensitivity in visual perception in the case of mesopic vision (twilight vision) and scotopic vision (night vision) and better testing can be carried out when there is high contrast between the surface to be examined and the excited fluorescences. What is problematic is that when carrying out the test methods by means of the known luminaires, when changing over between illumination with white light, which is used to inspect and assess defects found on the workpiece under the ultraviolet radiation, and illumination with ultraviolet radiation, a comparatively large change in brightness occurs to which the eyes have to adjust. Since the test is often accompanied by frequent changeover, the eyes are subjected to a comparatively great burden.